In a variety of applications, it is desirable to be able to determine the remaining volume of liquid in a container. In the medical field, for example, it is desirable to be able to determine the volume of reagent remaining in a source container used in automated clinical instrumentation. Determining the volume of saline or other liquid which remains in an intravenous infusion would also be advantageous.
A variety of means have been devised for permitting an attending physician or staff member to estimate the remaining liquid volume in a container. In the most basic form, containers have been provided with transparent walls and a graduated scale which is visible from the outside. However, the visual observation of liquid level is not always practical, such as when the container is not readily within the clinician's view. In addition, in some applications it may be desirable to have a more precisely quantitative indication of remaining liquid level or volume.
Thus, a variety of electronic liquid level detectors have been devised in the prior art. For example, U.S. Pat. No. 4,063,457 to Zekulin, et al. discloses an ultrasonic sensing device for mounting within a storage vessel such as a bilge or railroad tank car. The sensing device comprises an elongate tubular body to be vertically oriented within the tank car, having a port at the lower end to allow liquid to enter the tube and rise to the level of the liquid in the rest of the tank. Spaced apart vertically within the tube are a series of pairs of piezoelectric transducers which serve as transmitters and receivers of ultrasonic energy. Because ultrasonic energy propagates more readily through liquid than through air, the system can determine which pairs of piezoelectric transducers are below the liquid level and which pairs of piezoelectric transducers are above the liquid level. Thus, each piezoelectric pair serves to determine simply the presence or absence of liquid at that level.
Another submersible probe-type liquid level indicator is disclosed in U.S. Pat. No. 3,163,843 to Dieckamp. In this device, mechanical vibrations are propagated axially from a transducer through the probe which extends vertically within the liquid to be measured. Reflected transverse pulses are created at both the liquid surface and the submerged distal end of the probe, which are smaller in amplitude than the applied pulse. These reflected transverse pulses are propagated back to the transducer, and the waveforms of the various pulses are evaluated on an oscilloscope to determine the liquid level.
Another approach is disclosed in U.S. Pat. No. 4,144,517 to Baumoel. That patent discloses an externally mounted single transducer liquid level detector in which the presence or absence of liquid at a particular location of a tank or pipe is sensed through the wall of the container. The transducer can be secured to the outer surface of the container, such as by hand pressure, clamping or cementing. By comparing the rate of decay of the test signal following multiple wall reflections to known rate of decay values for filled and empty regions of the container, an output signal is produced which indicates the presence or absence of liquid in the container adjacent the transducer location.
In German Patent Application Number 3,703,658 to Schreiber, an ultrasonic signal is used to measure the level of liquid in a fuel tank for motor vehicles. Notwithstanding the foregoing, there remains a need for an improved volume sensor device which can be included in or externally mounted to a container and which can provide remaining liquid volume data on a continuous basis from empty through full. There also remains a need for adaptors for such volume sensor devices and for improved containers with which such devices can be used.